Movable center-blanked horizon line forming apparatus and saturable reactor pulse forming network for use therein



June 9, 1959 w, s 2,890,380

MOVABLE CENTER-BLANKED HORIZON LINE FORMING APPARATUS AND SATURABLEREACTOR PULSE FORMING NETWORK FOR USE THEREIN Filed Aug. 13, 1957 4Sheets-Sheet l 49 F|g.l. ,1"

r I 12. g 43 INVENTOR William F. List ATTORNEY June 9, 1959 Filed Aug.15, 1957 w. F. LIST I 2,890,380 MOVABLE CENTER-BLANKED HORIZON LINEFORMING APPARATUS AND SATURABLE REACTOR PULSE FORMING NETWORK FOR USETHERE'IN 4 Sheets-Sheet 2 A v A wdvnna a N v PrlmorylS WoveshopeResistor 2| Ll Ll Prim ory 26 A Woveshap. v \l k \l 7 Primary 32 l I V AI Wovuhope l I Terminol45 Woveshbpc 0 I90 200 M20 4C )O 50 0 BO O 7C2O80 0 900 Elac'rical Degrees Fil'ed Aug. 13, 1957 June 9, 1959 2,890,380

W. F. LIST MOVABLE CENTER-BLANKED HORIZON LINE FORMING APPARATUS ANDSATURABLE REACTOR PULSE FORMING NETWORK FOR USE THEREIN 4 Sheets-Sheet 3Amplifier Amplifier Intensify X AXIS Switch Y Axls Switch Z Axls SwitchSwitch Gate Generator June 9,1959 w. F. LIST MOVABLE CENTER-BLANKED2,890,380 HORIZON LINE FORMING APPARATUS AND SATURABLE REACTOR PULSEFORMING NETWORK FOR USE THEREIN 4 Sheets-Sheet 4 Filed Aug. 15, 1957 IZAwyill Time MOVABLE CENTER-BLANK'ED HORIZON LINE FORMING APPARATUS ANDSATURABLE RE ACTOR PULSE FORMING NETWORK FOR USE THEREIN William F.List, Linthicum Heights, Md., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication August 13, 1957, Serial No. 677,873

11 Claims. (Cl. 315-26) This invention relates to apparatus forgenerating a movable center-blanked horizon line for use in conjunctionwith a cathode ray tube breakaway cross symbol, and particularly to suchapparatus employing saturable reactors for obtaining pulses of thedesired wave forms needed in the production of the line and symbol.

As is well known in the art to which the invention pertains, it iscommon practice in aircraft to employ instruments for visually providingthe pilot with information regarding the attitude of the wings of theaircraft. One conventional type of such instrument employs movable ortiltable line forming means to indicate departure from the normal wingattitude, the movable line being associated with a large X or cross toprovide a breakaway command when the attitude of the aircraft wingsapproach the limits of safety, or some other hazard exists such asdangerous proximity to other aircraft or a ground obstruction, thehorizon line being center-blanked and rotating about a pointcorresponding substantially to the center of the breakaway cross or Xsymbol, to indicate the instant attitude of the wings of the aircraft,as aforestated.

The presentation of this information on a cathode ray tube typeindicator requires a special circuit for producing the center-blankedhorizon 'line, and heretofore the generation of the necessary pulses andsignal Wave shapes to provide the center-blanked movable horizon linehas required the use of a number of electron tu es with attendantcircuit complexities and limitations in the apparatus by reason of thesusceptibility of the tubes ,to excessive shock, acceleration and otherinfluences.

The apparatus of the instant invention overcomes the disadvantages ofthe prior art by employing saturable reactors in conjunction withsemiconductor diode recti- :fiBI'S and a number of resistors forgenerating pulses of the necessary shapes.

Accordingly, a primary object of the instant invention is to provide newand improved apparatus for generating .a center-blanked movable horizonline for use in conjunction with a breakaway cross symbol, forapplication to aircraft wing attitude indicators.

Another object is to provide a new and improved sat- :urable reactorcircuit for generating pulses having wave- .forms suitable for use inaircraft wing attitude indicators.

Other objects will become apparent after a study of the followingspecification when read in connection with the accompanying drawings, inwhich:

Figure 1 is a view of the display provided by apparatus embodying theinstant invention and including a cross or X to indicate a breakawaycommand and a movable center-blanked horizon line; i

Fig. 2 is a schematic electrical circuit diagram of apparatus employingsaturable reactors and diodes for producing pulses of the necessarywaveforms to provide for the indication of Fig. 1;

Fig. 3 is a graph of a number of pulse and voltage waveformsillustrating the operation of theapparatus of Fig. 2;

Fig. 4 is a schematic electrical circuit diagram largely 2,890,380Patented June 9, 1959 in block form, of apparatus for providing wingattitude information including the center-blanked horizon line and thebreakaway command symbol of Fig. 1; and

Figs. 5A, 5B, 5C and 5D are graphs or curves further illustrating theoperation of the apparatus of Figs. 1, 2 and 4.

Particular reference should be made now to the drawings, in which likereference numerals are used throughout to designate like parts, for amore detailed under standing of the invention and in particular to Fig.1 thereof. The reference numeral 10 generally designates the screen of acathode ray display tube shown in Fig. 4 and generally designated 11.The line 12, Fig. l, is the center-blanked horizon line which changesits slope in accordance with the variations in the attitude of the wingsof the aircraft, \and a large X symbol 13 is provided for indicating thedanger condition to be presented by the indicator, such as dangerousproximity to other aircraft;

Particular reference should be made now to Fig. 2 in which an electricalcircuit employing saturable reactors is shown for producing thenecessary pulse wave shapes to provide the indications of Fig. 1. Thereference numeral 14 generally designates a saturable reactor having aprimary winding 15, secondary windings 16, 17 and 18 which are providedfor purposes to be made hereinafter more clearly apparent, and asaturable core 19 which it is understood is composed of a suitablematerial which becomes saturated when the magnetic flux therein attainsa preselected value with the result that the impedance of the primarywinding varies markedly at saturation and that signals or voltagesinduced in the secondaries aforementioned vary markedly or quickly atthe moment of saturation, in a manner which will become hereinafter moreclearly apparent. One terminal of the primary 15 is connected by way oflead means 20 to a suitable source of substantially sinusoidal voltagewith reference to ground having a phase a as indicated by the curve A ofFig. 3. The other terminal of primary 15 is connected by way of lead 23and resistor 21 to ground 22. The last-named terminal 15 is alsoconnected by way of lead 23, resistor 24, and lead 25 to one terminal ofthe primary 26 of a secondary saturable reactor generally designated 27,the reactor 27 having a pair of secondaries 28 and 29 and a saturablecore 30. The other terminal of the aforementioned primary 26 isconnected to ground 22.

A. third saturable reactor generally designated 31 is provided having aprimary 32, secondaries 33 and 34 and saturable core 35. The terminalsof the primary 32 are connected, one terminal by way of resistor 36 andlead 37 and the other terminal by Way of lead 38 to a voltage ofsinusoidal wave form and of an amplitude corresponding to the amplitudeof the aforementioned voltage a applied to lead 20, and having a phasebe which lags the voltage fa by as indicated by graph A of Fig. 3.

The adjacent terminals of the aforementioned secondaries 33 and 3.4 ofsaturable reactor 31 are connected together by lead means 39 and toground 22. The other terminal of secondary 33 is connected by way oflead 40 to one terminal of the aforementioned secondary 17 of thesaturable reactor or transformer generally designated 14, and the otherterminal of secondary 17 is con nected to an output terminal 41. In likemanner, the other or lower terminal of the secondary 34 as seen in Fig.2 is connected by lead 42 to one terminal of the aforementionedsecondary 16 of the saturable reactor generally designated 14, and theother terminal of secondary 16 is connected to an output terminal 43.

The aforementioned secondary 18 of the saturable reactor or transformergenerally designated 14 has one terminal thereof connected to ground 22and the other terminal thereof connected by way of capacitor 44 to anoutput terminal 45. Output terminal 45 is also connectedby way ofresistor 46 to ground 22. The capacitor 44 and'resistor 46 form adifferentiating network which is provided for purposes to be madehereinafter more clearly apparent.

The aforementioned secondaries 28 and 29 of the aforementioned saturablereactor generally designated 27 have their adjacent terminals connectedto each other by way of lead 47 and to ground 22. The other terminal ofsecondary 28 is connected by way of resistor 48, lead 49 and rectifier50 to ground 22. Lead 49 is also connected by way of resistor 51 andlead 52 to an output terminal 53. The other terminal of theaforementioned secondary 29 is connected by way of resistor 54, lead 55and rectifier 56 to ground 22. Lead 55 is connected by way of resistor57 to lead 52. Lead 52 is further connected by way of resistor 58 toground 22. The aforementioned rectifiers 50 and 56 may be of the silicondiode type.

A transformer generally designated 59 is provided as shown in Fig. 2having a primary 60, a core 61 and a secondary 62. Core 61 is not of thesaturable type. One terminal of the primary is connected to ground 22,and the other terminal of the primary 60 is connected by way of lead 63across a suitable source of alternating current potential with referenceto ground of sine wave form having a phase b which lags phase "a" by 60,phase 11 being related to the aforementioned phases a and be asindicated by curves or graph A of Fig. 3. The voltage of phase 12 is ofsubstantially the same amplitude as the voltage of phases a and be. Thethree voltages having the phase relationships indicated by curves a, b,and be of graph A of Fig. 3 may be obtained by any convenient means, forexample, they may be obtained from a transformer connected to aconventional three-phase source.

The aforementioned secondary 62 of transformer 59 has one terminalthereof connected to ground 22 and the other terminal thereof connectedby way of resistor 64, lead 65 and capacitor 66 to ground 22. Lead 65 isconnected by way of capacitor 67, lead 68 and variable resistor 69 toground 22. Lead 68 is connected to one terminal of one winding 70 of aresolver generally designated 71, the other terminal of winding 70 beingconnected to ground 22. Resolver 71 has an energizing winding 72connected to any suitable source of potential, and an additional pair ofmovable windings 73 and 74, one terminal of each being connected toground 22, winding 73 having an output lead and winding 74 having anoutput lead 76. Suitable position means 77 is provided for positioningthe movable windings '73 and 74 of the resolver 71, and the positioningmeans 77 may be connected to a roll and bank responsive or controldevice which may be a gyro, as will be readily understood by thoseskilled in the art.

In the operation of the apparatus of Fig. 2, it should be recalled thatthe primary 15 of reactor or transformer 14 is connected across phase ain series with a resistor 21 shunted by the primary 26 of reactor 27 anda series resistor 24. The relative impedance of these branches arepreselected so that the load is effectively resistive. The voltageapplied to the circuit on the aforementioned lead 20 causes the voltageto build up sinusoidally across the primary 15 of reactor 14 until thecore 19 of this reactor saturates, when the voltage across the reactorprimary 15 falls to nearly zero because of the change in impedance ofthe primary windinng 15 at saturation. Pr or to this, the voltage acrossthe series resistor 21 was slowly increa n s u o d t h v ltss dividingproportionally to the impedagioes. Since the impedance o the p ma 15 isar rri r Q saturatin s'joliiiiaied to the value of resistor 21', thevoltage across the resistor former 27 is nearly zero prior to thesaturation of core 19. When saturation of the core 19 of reactor 14occurs, the voltage across the resistor 21 increases substantially tothe instantaneous value of the applied voltage on lead 20. The voltageacross the primary 26 of reactor 27 increases to substantially theapplied voltage level on lead 20 and follows sinusoidally until the core30 of reactor 27 saturates, thereby reducing the voltage across theprimary 26 of reactor 27 to substantially zero and causing the remainingportion of the applied wave shape to appear across the resistor 24 inseries with the primary 26. Voltage wave shapes are generated in thesecondaries 16, 17, 18, 28 and 29 of both of the reactors 14 and 27 bytransformer action. The uses of these secondaries will be disclosedinmore detail hereinafter.

in Fig. 3, to which particular reference is now made, the voltage acrossthe aforementioned primary 15 is shown .by curve B, the wave shape ofthe voltage across resistor 21 is shown by curve C, and the wave shapeof the voltage across the primary 26 is shown in curve D, in accordancewith the aforegoing explanation. The aforementioned secondaries 28 and29 of reactor 27 are con nected as aforedescribed in a manner such thatpositive pulses are attenuated through the series resistors and silicondiodes and only the negative pulses appear in the output on terminal 53.This output signal on terminal 53 is illustrated by the adjacent pulses,and is further illustrated by curve G of Fig. 3. Terminal 53 isconnected to the Z-axis switch of an intensity control circuit shown inFig. 4 and hereinafter toibe described in more detail.

The primary 32 of the aforementioned reactor 31 is connected in serieswith a current limiting resistor 36 and energized with voltage of phasebc" separated by 90 from phase a of curve A of Fig. 3. The voltage waveform across the primary 32 of reactor 31 behaves in a manner similar tothat of the previous description of the voltage waveform across theprimaries 15 and 26 of reactors 14 and 27 respectively. The secondaries33 and 34 of reactors 31 are interconnected as shown and aforementionedwith two of the secondaries, namely, 17 and 16 respectively of theaforementioned reactor or transformer 14 to form the'breakaway symbol,the voltage outputs of secondaries 16 and 17 being applied to terminals43 and 41, as shown, and having waveshapes as shown by graphs H and I ofFig. 3.

The remaining secondary winding 18 of reactor 14 is connected asaforementioned to a'ditferentiating circuit including capacitor 44 andresistor 46 to provide trigger pulses on output terminal 45 for amultivibrator or gate generator the indicator circuit of 'Fig. 4, such,for example, as a two hundred cycle multivibrator. The shape of thetriggering pulse at terminal 45, Fig. 2, is shown adjacent terminal 45and is further illustrated by curve F of Fig. 3.

The voltages for forming the aforementioned attitude line as seen at 12on screen 10, Fig. Lare generated in the above described circuit of Fig.2by supplying one winding of the aforementioned resolver "71 from phaseb through a two-section filter including resistor 64, capacitors 66 and67 and variable resistor 69. The variable resistor 69 makes it possibleto accurately center the blanking pulses about the signal voltage waveshape, as will be discussed in connection with Figs. SA-SD. The twooutput components of the resolver 71 as developed on the aforementionedleads 75 and 76 are connected to appropriate X axis and Y axis switchchannels, in a manner to be hereinafter more fully described inconnection with Fig. 4. i

It should be noted that the blanking pulses are preferably initiated atsubstantially 40 electrical degrees after the voltage of phase a haspassed the zero axis and are terminated at substantially 80electricaldegrees after the voltage of phase a has passed the zero axis. 'Thisresults 'in' the pulse starting 20 degrees before'and ending 20 degreesafter the voltage of phase b crosses the zero axis, it being recalledthat phase b lags phase a by 60 degrees.

Particular reference should be made now to Fig. 4 which shows anelectrical circuit diagram for utilizing the output pulses and voltagesfrom the apparatus of Fig. 2 to provide the indication shown in theaforementioned Fig. 1. V

In Fig. 4 there is shown a block generally designated 78, it beingunderstood that the block 78 includes the aforementioned transformer 59,the aforementioned filter circuit including resistors 64 and 69 andcapacitors 66 and 67 and the aforementioned resolver 71, the voltages onleads 75 and 76 being varied in accordance with movement of theaforementioned positioning means 77.

Three switches are provided for each of the three beam axes of theaforementioned cathode ray tube 11 including an aforementioned X axisswitch shown in block form and generally designed 80, an aforementionedY axis switch shown in block form and generally designated 81, and a Zaxis switch shown in block form and generally designated 82. Theswitches 80, 81 and 82 are provided and connected as shown, beingnecessitated because the breakaway or X signal 13 of Fig. l and thehorizon line 12 of Fig. l are alternately put on the screen of thecathode ray tube generally designated 11 in Fig. 4. All of the switches80, 81 and 82 have applied thereto on lead 83 a gating pulse obtainedfrom a gate generatoror multivibrator shown in block form and generallydesignated 84, the gate generator 84 being of any convenientdesign, forexample, a two hundred cycle multivibrator. The gate generator 84 isoperatively connected by lead 85 to the aforementioned output terminal45 of the pulse generator 79, and receives as an input a series oftriggering pulses such, for example, as those shown in Fig. 3F. Everypositive pulse from terminal 45 causes a switch gate to be generated at84, and this gate is applied by lead 83 to all three switches 80, 81,and 82 and operates the three switches simultaneously. Every time theswitches operate, they operate to alternately produce on the screen 10either the horizon line 12 or the breakaway symbol 13', in the mannerwhich will become hereinafter more clearly apparent. Any convenientswitching circuits could be employed at 80, 81 and 82, and constitute nopart of this invention.

A direct current voltage is supplied on lead 86 to the Z axis switch 82from a suitable source of direct current potential, now shown, which maybe of the order of 10 to volts and may, if desired, have the negativeterminal thereof connected to lead 86 and the positive terminal thereofconnected to ground 22, depending upon the circuit arrangement of theswitch and an associated amplifier hereinafter to be described.

The aforementioned outputs from the resolver 71 are applied by leads 75and 76 to the X axis switch 80 and the Y axis switch 81 respectively.Terminal 41 of the pulse generating apparatus of Fig. 2 is connected bylead 87 to the Y axis switch 81 whereas terminal 43 is connected by lead88 to the X axis switch 80. The aforementioned terminal 53 of theapparatus of Fig. 2 is connected by lead 89 to the Z axis switch 82. a

The output obtained from the X axis switch 80 is applied by lead means90 to an amplifier shown in block form and generally designated 91;-theoutput from the Y axis switch 81 is applied by lead means 92 to anamplifier shown in block form and generally designated 93; and theoutput of the Z axis switch 82 is connected by lead means 94 to anamplifier 95.

As aforementioned, a cathode ray display tube generally designated 11 isprovided, the tube 11 having a screen which may correspond to the screen10 of Fig. 1, having vertical deflection plates 96 and 97, horizontaldeflection plates 98 and 99, a cathode 100 and an intensity control grid101. The cathode 100 is connected to ground 22; the intensity controlgrid 101 is connected by lead 102 to the aforementioned amplifier thevertical deflection plates 96 and 97 are connected by leads 103 and 104to the aforementioned amplifier 93; and the aforementioned horizontaldeflection plates 98 and 99 are connected by leads 105 and 106 to theaforementioned amplifier 91.

Particular reference should be made now to Figs. 513- 5D inclusive, allthe curves of which are plotted on the same time base. Curve 5C showsthe aforementioned blanking pulses at terminal 53. In curve 5B, both thevoltages represented by thesolid line and the dashed line represent avoltage at the deflection plates which produces or paints a symbolindication. The solid line represents a properly phased voltage, and itwill be noted that the voltage represented by the solid line passesthrough zero at an instant corresponding substantially to the center ofthe corresponding blanking pulse of Fig. 50, whereas the improperlyphased voltage of the dashed line of Fig. 5B passes through zero at atime well ahead of the center of the blanking pulse.

The curve of Fig. 5D represents the combined results of the voltages ofFigs. 5B and 5C, and shows how the blanking pulses periodicallyeliminate portions of the voltage at the deflection plates.

In Fig. 5A, the center-blanked horizontal line indicates the attitudesymbol 12 at the scope, the portions of the attitude line beingdesignated 12A and 12B in Fig. 5A, the portions being of uniformbrightness throughout.

The lower broken or center-blanked horizon line of Fig. 5A representsthe results of improper phasing. Portion 12A is seen to have thin-linetail or end sections m and n, and line portion 12B is seen to havethin-end or tail sections p and q. Tail sections m, n, p, and q are ofdiminished brightness.

There has been provided then, apparatus well suited to perform andaccomplish the aforedescribed objects of the invention.

In some applications of the invention, for example, fire control, it isdesirable that the X symbol to provide a breakaway command not appear onscreen 10 until the dangerous condition occurs. In such applications,any convenient means, not shown, may be provided for applying a voltageon lead 86 for selective passage by the Z-axis switch 82 to intensitymodulatethe beam of cathode ray tube 11 and cause the X symbol 13 toappear in response to the occurrence of the dangerous condition.

Whereas for convenience of illustration a voltage of phase be laggingthe phase a by 90 degrees has been shown and described as energizing theprimary 32 of reactor-transformer 31, any sine wave voltage of properamplitude which lags the voltage of phase a by more than 40 degrees issuitable.

Whereas the line 12 has been referred to herein as a horizon line, itshould be understood that the line could be used to indicate the valueof any variable quantity supplied to the resolver 71 by means 77.

Whereas the invention has been shown and described with reference to anembodiment thereof which gives satisfactory results, it should beunderstood that modifications may be made and equivalents substitutedwithout departing from the spirit and scope of the invention.

I claim as my invention:

1. In cathode ray tube indicator apparatus for providing an indicationof a movable center-blanked line symbol and a fixed breakaway symbol, incombination, cathode ray tube means, signal obtaining means includingresolver means and saturable reactor means for obtaining a plurality ofsignals having a plurality of preselected wave shapes and a plurality ofpreselected time relationships therebetween, and means operativelyconnected to the signal obtaining means and to the cathode ray tubemeans for alternately applying some of said signals and the remainder ofsaid signals to said cathode ray tubemeans, said cathode ray tube meansbeing constructed and arranged to utilize the signals applied thereto toalternately provide said movable line symbol and fixed breakaway symbol.

2. In cathode ray tube indicator apparatus for providing a movable'lirie symboland a breakaway symbol in conjunction therewith'jincombination, first signal obtaining means for providing a pair ofsignals having preselected wave shapes, amplitudes 'and timerelationships With respect to each other, means operatively connected tosaid first signal obtaining means for altering said pair of signals inaccordance with variations in'a variable quantity, saturable reactorsignal obtaining means for providing a plurality of other signals havingpreselected amplitudes, wave shapes and time relationships therebetween,cathode ray tube means, and means operatively connected to the firstsignal obtaining means, to the cathode ray tube means, and to thesaturable reactor signal obtaining means for alternately applying saidpair of signals and said plurality of other signals to said cathode raytube means, said cathode ray tube means being constructed and arrangedto utilize the pair of signals to provide a movable line symbol and saidother signals to provide said breakaway symbol.

3. In cathode ray tube indicator apparatus for providing a movable linesymbol in conjunction with a breakaway symbol, in combination, cathoderay tube means, voltage obtaining means adapted to have applied theretoa variable input corresponding to the instant value of a variablequantity, said voltage obtaining means being constructed and arranged toutilize the variable input to provide a pair of variable voltages,saturable reactor means for obtaining a plurality of signals having aplurality of preselected wave shapes, amplitudes and time relationshipstherebetween, and switching means alternately operatively connectingsaid voltage obtaining means and said saturable reactor means to saidcathode ray tube means, said cathode ray tube means being constructedand arranged to utilize the voltages and signals applied thereto toprovide the line and breakaway symbol indications.

4. Apparatus for providing a movable line indication of a variablequantity and a stationary indication adjacent thereto which is adaptedto establish limits for the variable quantity comprising, incombination: cathode ray tube means, first signal obtaining meansincluding saturable reactor pulse forming means, switching means, meansincluding said switching means operatively connecting said first signalobtaining means to said cathode ray tube means, said cathode ray tubemeans being constructed and arranged while some of the signals from thefirst signal obtaining means are applied thereto to produce saidstationary indication, second signal obtaining means adapted to have avariable input applied thereto which varies in accordance withvariations in the quantity to be indicated, and means including saidswitching means operatively connecting said second signal obtainingmeans to said cathode ray tube means, said cathode ray tube means beingfurther constructed and arranged to utilize the signals from the secondsignal obtaining means and at least some of the pulses from thesaturable reactor pulse forming means to provide said movable lineindication with a predetermined portion thereof blanked out.

5. Apparatus for providing a movable line indication of a variablequantity and a stationary indication adjacent thereto comprising, incombination, cathode ray tube means including switching means and acathode ray tube, first signal obtaining means including saturablereactor pulse forming means operatively connected to said cathode raytube means for obtaining first signals including signals for providingthe stationary indication, and second signal obtaining means adapted tohave a variable input applied thereto which varies in accordance withvariations in the quantity to be indicated and to provide variablesecond signals for forming said movable line indication, said secondobtaining means being operd d at -E t s l9 t il Pfitl sttls ray tub measaid switching means providing for alternate use by the cathode'ray tubeof signals from the second signal obtaining means and some of thesignals from the first signal obtaining means, said cathode ray tubemeans being constructed and arranged to utilize other of the signalsfrom the first signalobtainin'g means .to' blank out a predeterminedportion of said line indication.

6. In apparatus for providing a movable line indication of avariablequantity, in combination, cathode ray tube means including means adaptedto have a variable input applied thereto which varies in accordance withvariations in the quantity to be indicated and to pro vide variablesignals for utilization by the remainder of the cathode ray tube meansto provide said movable line indication, and saturable reactor pulseforming means operatively connected to said cathode ray tube means, saidcathode r b ns bein construc ed and arra ge to ut ize th pul f o the stura re ctor p e o ing means to blank out a predetermined portion ofsaid line.

7. In apparatus for providing a movable line indication of a variablequantity, in combination, cathode ray tube means, means adaptedto have avariable input applied thereto which varies in accordance withvariations in the quantity to be indicated, said last-named means beingoperatively connected to said cathode ray tube means and constructed andarranged to provide a variable signaloutput to the cathode ray tubemeans, said cathode ray tube means being constructed and arranged toutilize the variables ignal output to provide said movable lineindication, saturable reactor means for obtaining pulses havingpreselected characteristics and predetermined time relationships to said'variable signal output, and means operatively connecting said saturablereactor means to said cathode ray tube means, said cathode ray tubemeans being" further constructed and arranged to utilize said pulses toblank out a predetermined portion of said line.

8 In apparatus for providing 'amovable line indication of a variable'quantity, 'in'combination, resolver means adapted'to have a variableinput applied thereto which varies in accordance with variations in thequantity to be indicated, said resolver means being constructed andarranged to provide two variable signal voltages, cathode ray tube meanshaving vertical and horizontal deflection plates and intensity controlmeans, means operatively connecting said resolver means to said cathoderay tube means, said cathode ray tube means having said two signalvoltages applied to the vertical and horizontal deflection platesthereof and utilizing said two signal voltages to form said movableline,'s'atur able reactor means for forming pulses having a preselectedpolarity, ampli tude, and wave shape and a predetermined timerelationship to said two signal'voltages, and means operativelyconnecting said saturable reactor means to said intensity control meansin a manner whereby said pulses blank out a predetermined portion ofsaid line.

9. Apparatus for providing a movable line indication of a variablequantity and a stationary indication adjacent thereto comprising, incombination, cathode ray tube means including switching means,first'satur'able reactor signal obtaining means operatively connectedtos'aid cathode ray tube means, said cathode ray tube means beingconstructed and arranged to utilize first signals from the firstsaturable reactor signal, obtaining means to provide the stationaryindication in accordance with the setting of the switching means, othersignal obtaining means operatively connected to the cathode ray tubemeans and adapted to'ha've a variable input applied thereto which variesin accordance 'with variations in the quantity to be indicated and toprovide variable second 'signals'fo'r forming said movable lineindication in accordance'with the setting of the "switching means, saidswitching means providing for alternate use by the cathode ray' tubemeans of the first and second signals, second satljrable' reactor meansoperatively connected to the first saturable' reactor means forobtaining blanking pulses having predetermined time relationships to thefirst and second signals, and means operatively connecting the secondsaturable r'eactor means to said cathode ray tube means, said switchingmeans passing said blanking pulses simultaneously with the passage ofsaid second signals, said cathode ray tube means being constructed andarranged to utilize the pulses from the second saturable reactor meansto blank out a predetermined portion of said line.

10. In cathode ray tube indicator apparatus, in combination, firstvoltage obtaining means for obtaining first and second voltages havingpreselected wave shapes, cathode ray tube means including a pair ofvertical deflection plates, a pair of horizontal deflect-ion plates, andan intensity control grid, first and second switching meansinterconnecting said first voltage obtaining means and said cathode raytube means, said first and second switching means being adapted while inpreselected settings to apply said first and second voltages to saidpairs of deflection plates to provide a line indication on the screen ofsaid cathode ray tube means, other voltage obtaining means includingsaturable reactor means for obtaining other voltages, said other voltageobtaining means being connected to said first and second switchingmeans, third switching means interconnecting said other voltageobtaining means and said cathode ray tube means, said other voltageobtaining means providing a blanking voltage which, while said thirdswitching means is in a preselected setting, is applied to saidintensity control grid to blank a portion of the line indication on thescreen of said cathode ray tube means, said other voltage obtainingmeans also providing a series of trigger pulses, a switch gate generatoroperatively connected to said other voltage obtaining means to have saidtrigger pulses applied thereto and providing for the generation of aswitch gate upon the application thereto of at least certain ones ofsaid trigger pulses, means connecting said switch gate generator to allof said first, second, and third switching means to operate the same,said switching means being constructed and arranged to alternately applyto the deflection plates of said cathode ray tube means voltages fromthe first voltage obtaining means and some of the voltages from theother voltage obtaining means, said other voltage obtaining means whilethe remainder of the voltages therefrom are applied to said cathode raytube means providing for the generation of a cross symbol on the screenof said cathode ray tube means.

11. Apparatus for use on aircraft for providing a movable center-blankedhorizon line and a breakaway cross symbol cfor use in conjunction withsaid line to indicate to the pilot of the aircraft that variation of thehorizon line from its normal position has passed a safe limitcomprising, in combination, cathode ray tube means including a viewingscreen, a pair of vertical deflection plates, a pair of horizontaldeflection plates, and an intensity control grid, means :forming an Xaxis switch, a Y axis switch, and a Z axis switch, means operativelyconnecting all of said switches to said cathode ray tube means,

each of said X, Y, and Z axis switches having first and second settings,voltage obtaining means for obtaining a pair of voltages, meansoperatively connecting said X axis switch and said Y axis switch to saidvoltage obtaining means for applying one voltage of the pair to each ofthe X and Y axis switches, other voltage obtaining means includingsaturable reactor means for obtaining a blanking pulse, means connectingsaid Z axis switch to said other voltage obtaining means for applyingthe blanking pulse to the Z axis switch, said X, Y and Z switches beingconstructed and arranged while in first settings thereof to apply saidpair of voltages and said blanking pulse to the deflection plates andintensity control grid of said cathode ray tube means to provide acenter blanked horizon line, said voltage obtain-ing means includingmeans adapted to have a variable turning input applied thereto forcausing the horizon line to rotate about its center point, said othervoltage obtaining means being operatively connected to said X axisswitch and said Y axis switch, said X axis switch and said Y axis switchbeing constructed and arranged while in second settings thereof to applythe voltages from the other voltage obtaining means to the horizontaland vertical deflection plates, the voltages from said other voltageobtaining means having preselected characteristics and causing an Xsymbol to appear on the screen of said cathode ray tube means, saidother voltage obtaining means including means for providing a series oftrigger pulses having predetermined time relationships to the voltagesfrom the Voltage obtaining means and the voltages from the other voltageobtaining means, and switch gate generator means operatively connectedto the other voltage obtaining means and having said trigger pulsesapplied thereto, said switch gate generator means being constructed andarranged to utilize at least some of the trigger pulses to provideswitching gates, said switch gate generator means being operativelyconnected to all of said X, Y and Z axis switches, said X, Y and Z axisswitches being further constructed and arranged to utilize the switchinggates to alternate between first and second settings to therebyselectively connect the ouput of the voltage obtaining means and theblanking pulse from the other voltage obtaining means to said cathoderay tube means, and thereafter selectively connect only the othervoltages from the other voltage obtaining means to said cathode ray tubemeans.

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